The only SMS I can receive is from a relative's mobile, but no one else.

[ConstantlyAngry]

SMS messages are not coming through, except for one relative. All other texts never arrive.

[japitts]

Does that include messages sent from your phone to itself?

[Oxonian · Accepted solution]

This might help @ConstantlyAngry :-

Guide: Text Message Tips (not sent or received) 

[ConstantlyAngry]

Forcing the phone to try to connect to other networks in 'Settings' seems like a weird thing to do, especially when they're described as 'unavailable' to O2 users, however this was the solution. It still doesn't explain WHY it occurred. Minding your own business, then suddenly, strange behaviour deprives you of your expensive, paid-for service...

[Enlli]

Forcing the phone to try and connect to another network is like a hard reset for your mobile connection.

Surprising the number of problems I've seen it sort out over the years, and not just O2

[jonsie]

It's like the traffic lights changing to green and all the backed up texts can flow freely

[Oxonian]

Glad that's resolved @ConstantlyAngry ! 👍